Process for the production of black colloidal-silver dispersion



United States Pate PRUCESS FOR THE PRGDUCTION F BLACK CQLLOHDAL-SILVER DISPERSIGN Yahachi Terashima and Yukio Yasuda, Ashigara-Kamigun, Kanagawa, Japan, assignors to Fuji Shashin Film Kabushiki Kaisha, Ashigara-Kamigun, Kanagawa, Japan No Drawing. Filed Oct. 29, 1965, Ser. No. 505,734 Claims priority, application Japan, Nov. 9, 1964, 39/ 63,103 Int. Cl. G031: 1/84 US. Cl. 1061 6 Claims ABSTRACT OF THE DISCLOSURE A process for producing black colloidal-silver dispersions which comprises reacting a silver halide emulsion formed in a hydrophilic protective colloid with 0.0001 to 0.1 mole of borohydride per mole of silver halide in the emulsion, about 0.08 to 80 percent of the equivalent weight of the borohydride required to reduce all of the silver halide being present. A photographic developer is also present as a reactant.

The present invention relates to a process for the production of black colloidal-silver dispersion.

It has hitherto been known that a black colloidal-silver dispersion is useful for providing antihalation layers of photographic elements or neutral gray optical filters or optical wedges.

The antihalation layer to be used for photographic elements, particularly for color photographic sensitive elements, must have a sufficiently high optical density to incident light from the surface of an emulsion layer in a visible region (particularly in a red region) and further must have a sufficiently low reflectance to the incident light from the emulsion layer surface of the photographic sensitive element. Furthermore, it is necessary that the antihalation layer not adversely influence the adjacent photographic emulsion layers and be completely decolorized by a conventional bleaching bath.

Conventionally known colloidal-silver dispersions give almost no bad influences on emulsion layers and have almost satisfactory properties about the decoloration, but they have such drawbacks that the optical density to red light is low and the reflectance of it is considerably high.

It has been known that there is a definite relation between the size of particles dispersed in a colloidal-silver dispersion and the optical density thereof (e.g., E. Klein; Photo. Sci. Eng, vol. 5, -ll (1956)).

If the colloidal-silver particle is fine, the storage stability of a dispersion of the colloidal-silver particle is high but the absorption spectrum of the dispersion is yellowyellowish brown and hence the optical density to red light is low.

On the other hand, a dispersion containing a coarse colloidal-silver particle assumes a black-brown color and the optical density to red light is considerably high, but the reflectance is high, and also the storage stability of the dispersion is low.

Processes for producing colloidal-silver dispersions are disclosed, for example, in US. Patent 2,688,601, a method wherein a soluble silver salt is reduced by hydroquinone and in German Patent 1,096,193, a method wherein a weak-soluble silver salt is reduced by hydrazine. However, since the colloidal-silver dispersions produced by these known processes have insufiicient optical density to red light or have a high reflectance, the properties of the dispersions are unsatisfactory as colloidal-silver dispersions for antihalation layers.

Therefore, an object of this invention is to provide a process for producing a black colloidal-silver dispersion having a low reflectance and a high optical density.

Another object of this invention is to provide an improved colloidal-silver dispersion having a low reflectance and a high optical density to red light.

Still another object of this invention is to provide a photographic element, particularly a color photographic element, having an improved antihalation layer having a high optical density to red light and a low reflectance to incident light from the surface of an emulsion layer and also having no bad effect on adjacent photographic emulsion layers.

According to the present invention, the black colloidalsilver dispersion is produced by reacting a silver halide emulsion formed in a hydrophilic protective colloid with borohydride and a photographic developer.

The silver halide emulsion to be used in this invention may be prepared by any known conventional methed for producing photographic silver halide emulsions. As a silver halide there may be used silver chloride, silver bromide, silver bromochloride, silver bromoiodochloride, silver iodochloride, silver bromoiodide, and the like. As the hydrophilic protective colloid materials usually known in the production of conventional photographic silver halide emulsions, such as, an aqueous solution of gelatin, polyvinyl alcohol, or a water-soluble cellulose may be used. When borohydride is added in the above-mentioned silver halide emulsion, a part of the silver halide is reduced to give suitable developing nuclei to the silver halide particles. The borohydride may be used as the form of an alkali metal salt, such as a potassium salt, sodium salt and ammonium salt or of other water-soluble metal salts. It is suitable to use such a borohydride as an aqueous alkali solution.

The silver halide emulsion having suitable developing nuclei is then completely reduced by the action of the photographic developer into black colloidal silver. As the photographic developer there may be used any well known developer, such as hydroquinone, toluhydroquinone, catechol, monomethylaminophenol, 1-phenyl-3- pyrazolidone, phenylenediamine, ascorbic acid, and hydrazine. Besides the developer, a caustic alkali, sodium carbonate, potassium carbonate, borax, sodium metaborate, sodium phosphate, sodium sulfite and the like may be used as an alkali agent.

The effective addition amount of the borohydride used in this invention is 0.0001-0.1 mol, particularly 0001- 0.05 mol per 1 mol of a silver halide in the emulsion. If the amount is less than the range, the optical density is too low and if the amount is higher than the value, the dispersion becomes a yellow colloidal-silver dispersion. In both cases, then, a dispersion having a high optical density to red light is unobtainable.

The colloidal-silver dispersion produced according to the present invention may be added with a thiol compound or an organic compound capable of forming a thiol compound by being easily decomposed to further improve the storage stability, if necessary.

In the case of producing a colloidal-silver dispersion from a silver chloride or silver bromochloride emulsion by the process of this invention, by adding into the emulsion preliminary a benzotriazol derivative, such as 6-nitrobenzotriazol, -methylbenzotriazol, 6-sulfobenzotriazol, 4'-nitro-naphtho-1',2-4,5triazol and the like, a colloidal-silver dispersion having higher red optical density can be easily obtained.

For removing the excessive developer or the oxidation products thereof from the colloidal-silver gelatin dispersion obtained by reducing a silver halide emulsion, the dispersion is gelled by cooling, cut into fine pieces, and rinsed with water. Instead of applying such a process, the

colloidal-silver gelatin dispersion is added with, as precipitating agent, organic solvents as shown in U.S. Patent 2,982,652 or anion surface active agents as shown in U.S. Patent 2,489,341 to separate by precipitating the gelatin containing colloidal silver and remove unnecessary developer.

The process of this invention is illustrated in the following examples:

Example 1 Into 400 parts (by weight) of a 5% aqueous gelatin solution was added 50 parts of a 15% aqueous potassium bromide solution and while maintaining the solution at 50 C., 1000 parts of a aqueous silver nitrate solution at 40 C. was added into the solution with a constant addition rate in 10 minutes. After allowing to stand for a further minutes, the solution was added with 400 parts of gelatin and 600 parts of water and the system was allowed to stand for 1 hour at 50 C. Into the solution was added 80 parts of a solution of 0.08 part of potassium borohydride in 100 parts of a 1.5% caustic soda and then was added an aqueous solution of 7 parts of monomethylaminophenol sulfate, 18 parts of hydroquinone, 100 parts of sodium sulfite (anhydrous), 80 parts of sodium carbonate (anhydrous), and 10 parts of caustic soda in 1500 parts of water as a developer. After allowing to stand for 15 minutes, the system was added with 360 parts of a 10% aqueous sulfuric acid solution and, after cooling, thus obtained colloidal-silver dispersed gelatin solution was set. The product was cut into fine pieces, which were sufiiciently washed with cold water until sulfate ion became undetectable.

Thereafter, 100 parts of thus obtained colloidal-silver dispersed gelatin gel was dissolved in water by heating. The solution was added with 2 parts of a 5% chromium acetate solution and applied on a transparent film support and dried to give the amount of coated silver of 0.70 g./ sq. In.

For comparing the colloidal-silver dispersion obtained in the example with colloidal-silver dispersions produced by conventional methods, two colloidal-silver dispersions were prepared as follows. That is, the one was prepared by directly reducing an aqueous gelatin solution of silver nitrate by hydroquinone and the other was prepared as in the above example except that parts of 10% caustic soda and 80 parts of aqueous 1% hydrozine sulfate solution were added in the silver halide emulsion instead of adding potassium borohydride. Each of the colloidal-silver dispersions was applied also on a transparent film sup port and dried to give the amount of coated silver of 0.70 g./sq. m.

The optical densities and refiectances of these colloidalsilver dispersions are shown in the following table:

TABLE 1 Into 240 parts of a 2% aqueous solution of gelatin were dissolved 14 parts of potassium bromide and 1 part of potassium iodide and while maintaining the solution at 60 C., 200 parts of a 10% aqueous solution of silver nitrate at 50 C. was added with a constant addition rate in 5 minutes. After allowing to stand for 10 minutes, the solution was added with 100 parts of gelatin and 100 parts of water and the system was kept at 60 C. until the gelatin was completely dissolved.

Thereafter, the solution was allowed to cool to 45 C. and added with a solution of 0.08 part of sodium borohydride in parts of 1.5% caustic soda in various proportions (0.6 part to 600 parts) and then with an aqueous solution of 0.3 part of 1-phenyl-3-pyrazolidone, 3 parts of hydroquinone, 15 parts of sodium sulfite (anhydrous), 25 parts of trisodium phosphate and 2 parts of caustic soda in 350 parts of water as a developer. After allowing to stand for 15 minutes, the solution was added with 50 parts of a 0.3% methanol solution of Z-mercaptobenzoimidazol and then 50 parts of a 10% aqueous solution of sulfuric acid and set by cooling to the gelatin gel containing the colloidal-silver dispersion, which was cut into fine pieces and washed with water. The waterwashing was continued until the sulfate ions became undetectable.

Thus obtained colloidal-silver dispersion was applied on a support as in Example 1. The optical density and reflectance are shown in the following table:

TABLE 2 Optical density Reflectance, percent Sodium boromol/1 mol hydride (part) AgX 650 mp. 550 mp 650 mp 550 my 1 07 1o- 0. 82 0. 89 4. 7 4. 3 3 57 10- 1.00 0. 09 3.0 3.1 1 07x10 1.17 1.12 2.6 2. 8 3 57 10- 1. 32 1. 39 2. 6 2. 6 1. 07) l0- l. 32 1. 74 2.6 2.6 3. 57x10 1.10 1. 69 2. 4 2. 5 1. 07 10- 0. 45 0. 99 2.0 2. 1

Example 3 Into 240 parts of a 2% aqueous solution of gelatin was dissolved 10 parts of sodium chloride and while maintaining the solution at 60 C., 200 parts of a 10% aqueous solution of silver nitrate at 50 C. was added into the solution with a constant addition rate in 10 minutes. After allowing to stand for 10 minutes, 100 parts of gelatin and 100 parts of water were added into the solution and the system was maintained at 60 C. until the gelatin was completely dissolved. The solution was allowed to cool to 45 C. and added with 30 parts of a 1% methanol solution of 6-nitrobenzotriazol and 20 parts of a solution of 0.08 part of sodium borohydride in 100 parts of 15% caustic soda. Into the solution was added an aqueous solution of 0.3 part of l-phenyl-S-pyrazolidone, 3 parts of hydroquinone, 15 parts of sodium sulfite (anhydrous), 25 parts of trisodium phosphate, and 2 parts of caustic soda in 350 parts of water as a developer.

After allowing to stand for 15 minutes, the solution was added with 50 parts of a 0.3% methanol solution of Z-mercapto-benzoimidazol and, after adding further 50 parts of a 10% aqueous solution of sulfuric acid, set by cooling to give a gelatin gel containing thus obtained colloidal-silver dispersion, which was cut into fine pieces and washed with water until the sulfate ions became undetectable.

Thus obtained colloidal-silver dispersion was applied on a support as in Example 1. The optical density was 0.96 at 650 me and 0.96 at 550 me and the reflectance was 2.8% at 650 Ill/.6 and 3.2% at 55011111..

What is claimed is:

1. A process for the production of a black colloidalsilver dispersion which comprises reacting a silver halide emulsion formed in a hydrophilic protective colloid with 0.0001 to 0.1 mol of borohydride per 1 mol of the silver halide in the emulsion and then with a photographic developer.

2. The process as claimed in claim 1 wherein said hydrophilic protective colloid is selected from gelatin, polyvinyl alcohol and a water-soluble cellulose.

3. The process as claimed in claim 1 wherein said borohydride is selected from sodium borohydride, potassium borohydride, and ammonium borohydride.

4. The process as claimed in claim 1 wherein said photographic developer is one selected from the group consisting of hydroquinone, toluhydroquinone, catechol, monomethylaminophenol, 1-pheny1-3-pyrazolidone, phenylenediamine, ascorbic acid, hydrazine, and derivatives thereof.

5. The process as claimed in claim 1 wherein the reaction mixture is further added with a benzotriazol derivative.

6. The process as claimed in claim 5 wherein said benzotriazol derivative is selected from the group consisting of 6-nitrobenzotriazol, 6-methylbenzotriazol, 6-sulfobenzotriazol, 4-nitro-naphtho-1,2-4,5-triazol.

6 References Cited UNITED STATES PATENTS 2,461,661 2/1949 Schlesinger et a1. 75108 2,806,798 9/1957 Weaver 96-84 3,082,079 3/1963 Bulloch et a1. 75108 3,334,995 8/1967 Gaspar 75-108 NORMAN G. TORCHIN, Primary Examiner RONALD H. SMITH, Assistant Examiner 10 US. Cl. X.R. 96-84; 106-137 

